1 files changed, 68 insertions, 0 deletions
diff --git a/rust/kernel/pid_namespace.rs b/rust/kernel/pid_namespace.rs
new file mode 100644
index 000000000000..0e93808e4639
--- /dev/null
+++ b/rust/kernel/pid_namespace.rs
@@ -0,0 +1,68 @@
+// SPDX-License-Identifier: GPL-2.0
+
+// Copyright (c) 2024 Christian Brauner <brauner@kernel.org>
+
+//! Pid namespaces.
+//!
+//! C header: [`include/linux/pid_namespace.h`](srctree/include/linux/pid_namespace.h) and
+//! [`include/linux/pid.h`](srctree/include/linux/pid.h)
+
+use crate::{
+    bindings,
+    types::{AlwaysRefCounted, Opaque},
+};
+use core::ptr;
+
+/// Wraps the kernel's `struct pid_namespace`. Thread safe.
+///
+/// This structure represents the Rust abstraction for a C `struct pid_namespace`. This
+/// implementation abstracts the usage of an already existing C `struct pid_namespace` within Rust
+/// code that we get passed from the C side.
+#[repr(transparent)]
+pub struct PidNamespace {
+    inner: Opaque<bindings::pid_namespace>,
+}
+
+impl PidNamespace {
+    /// Returns a raw pointer to the inner C struct.
+    #[inline]
+    pub fn as_ptr(&self) -> *mut bindings::pid_namespace {
+        self.inner.get()
+    }
+
+    /// Creates a reference to a [`PidNamespace`] from a valid pointer.
+    ///
+    /// # Safety
+    ///
+    /// The caller must ensure that `ptr` is valid and remains valid for the lifetime of the
+    /// returned [`PidNamespace`] reference.
+    pub unsafe fn from_ptr<'a>(ptr: *const bindings::pid_namespace) -> &'a Self {
+        // SAFETY: The safety requirements guarantee the validity of the dereference, while the
+        // `PidNamespace` type being transparent makes the cast ok.
+        unsafe { &*ptr.cast() }
+    }
+}
+
+// SAFETY: Instances of `PidNamespace` are always reference-counted.
+unsafe impl AlwaysRefCounted for PidNamespace {
+    #[inline]
+    fn inc_ref(&self) {
+        // SAFETY: The existence of a shared reference means that the refcount is nonzero.
+        unsafe { bindings::get_pid_ns(self.as_ptr()) };
+    }
+
+    #[inline]
+    unsafe fn dec_ref(obj: ptr::NonNull<PidNamespace>) {
+        // SAFETY: The safety requirements guarantee that the refcount is non-zero.
+        unsafe { bindings::put_pid_ns(obj.cast().as_ptr()) }
+    }
+}
+
+// SAFETY:
+// - `PidNamespace::dec_ref` can be called from any thread.
+// - It is okay to send ownership of `PidNamespace` across thread boundaries.
+unsafe impl Send for PidNamespace {}
+
+// SAFETY: It's OK to access `PidNamespace` through shared references from other threads because
+// we're either accessing properties that don't change or that are properly synchronised by C code.
+unsafe impl Sync for PidNamespace {}